The present invention relates to a wafer support member used in fixing, straightening, conveying and the like of wafers in, for example, a semiconductor manufacturing apparatus.
The wafer support member is used in a semiconductor manufacturing apparatus in the process of fixing the semiconductor wafer which is the object of attraction for PVD, CVD, etching, or other processing, or attracting and fixing the semiconductor wafer for straightening the warp, or attracting and conveying the semiconductor wafer.
In the structure of such wafer support member, as shown in FIG. 1, the surface of a ceramic body 11 in which an internal electrode 12 is buried in a attraction surface 11a, and the ceramic body 11 is bonded to a base plate 13 made of metal. By applying a voltage between the internal electrode 12 and attraction object 20, an electrostatic attraction force is generated, and the and the attraction object 20 is attracted and fixed to the attraction surface 11a.
Bonding to the base plate 13 is intended to facilitate assembly into devices, and to cool the attraction object 20 such as wafer by incorporating cooling mechanism (not shown) in the base plate 13. Between this metallic base plate 13 and ceramic body 11, an adhesive layer 14 of metalized compound, organic solvent or glass is interposed to bond, but when temperature change occurs, the ceramic body 11 may be broken due to difference in thermal expansion between the metallic base plate 13 and ceramic body 11.
It is hence attempted to decrease the difference in thermal expansion with the ceramic body 11 by composing the base plate 13 by using metal of low thermal expansion such as tungsten (W), molybdenum (Mo) and Kovar. Or the present applicant proposed to use aluminum (Al) for the base plate 13 and silicone adhesive for the adhesive layer 14 so as to absorb the difference in thermal expansion (Japanese Laid-open Patent 2-287344).
When tungsten or molybdenum is used as the base plate 13, however, processability is poor, and it is hard to incorporate cooling mechanism inside, and it is expensive. Using Kovar, meanwhile, since the thermal conductivity is not high, the cooling effect of the attraction object 20 such as wafer is poor.
On the other hand, by bonding the ceramic body 11 and base plate 13 with the adhesive layer 14 composed of silicone adhesive, the thermal conductivity of the silicone adhesive is relatively low, and if the adhesion thickness fluctuates, it is hard to maintain the wafer or other attraction object 20 at uniform temperature. Along with high speed trend of the wafer processing step, a high electric power is required, for example, in plasma etching, but the wafer cannot be cooled sufficiently in the case of using silicone adhesive.
The invention is intended to compose the wafer support member by bonding the ceramic body having an attraction surface in which an internal electrode is buried, and the base plate, through an adhesive layer composed of indium or indium alloy.
That is, the indium or indium alloy is high in thermal conductivity, and is a flexible metal, and it can release the heat applied to the wafer or attraction object uniformly and quickly, and also absorb the difference in thermal expansion between the ceramic body and base plate.
The invention hence relates to the attraction device such as wafer support member or vacuum chuck used in fixing, heating, filming or processing of silicon wafer in a semiconductor manufacturing apparatus.
In the semiconductor manufacturing apparatus, hitherto, the vacuum chuck or wafer support member has been used as the silicon wafer stage, and in particular the wafer support member is preferably used because it can easily express the flatness or parallelism of the processing surface required at the time of fine processing of wafer in general vacuum.
Moreover, along with the sophistication of degree of integration of semiconductor element, a higher precision is required also in the wafer support member, and a ceramic-made wafer support member has come to be used.
Such high precision ceramic-made wafer support member has been manufactured by sintering integrally by incorporating a conductive layer forming an internal electrode in alumina ceramics (see Japanese Laid-open Patent 62-264638).
In the manufacturing process of semiconductor accompanied by vapor deposition or etching, a halogen derivative plasma is often used, and it is recently proposed to use aluminum nitride ceramics excellent in plasma resistance (Japanese Laid-open Patent 6-151332).
Since, however, other components than AlN are contained in aluminum nitride ceramics, high purity and high density are demanded in the aluminum nitride in order to enhance the plasma resistance. The aluminum nitride film obtained by vapor phase growth method is known to comply with such requirements and be free from adverse effects such as contamination of wafer.
It is hence proposed to obtain a wafer support member excellent in plasma resistance by printing a metal paste as electrode in a specific pattern on a green sheet of ceramics such as alumina and aluminum nitride, laminating and sintering into one body, and forming an aluminum nitride film on the surface of this base body by vapor phase growth method.
Alternatively, the base body may be composed of conductive metal or ceramics, and the wafer support member may be constituted by forming an aluminum nitride film on the surface of the base body as insulating layer.
In any means, the aluminum nitride film must be pure and dense, and the vapor phase growth method is indispensable as the film forming method.
Nevertheless, in the wafer support member forming an aluminum nitride film on the surface, the aluminum nitride film formed by the vapor phase growth method is a uniform and homogeneous film on a horizontal surface, but a sufficient film thickness is not obtained on a vertical surface, such as outer circumference and inner wall of penetration hole.
That is, the wafer support member has an outer circumference, and also penetration holes such as pin holes for moving the attracted wafer or gas holes for leading in gas such as helium, and the aluminum nitride film formed in such vertical surfaces as the outer circumference and inner wall of penetration holes is extremely thin. Hence, by short-time etching by plasma, the base body is exposed on the vertical surface, especially in the edge, and the plasma resistance is impaired.
Recently, moreover, in the trend of higher density of integrated circuit and shorter time of plasma processing, the plasma density increases progressively. By contrast, there has been no wafer support member capable of maintaining an excellent plasma resistance owing to the reasons stated above.
In the invention, accordingly, the base body having penetration holes opening in a flat plane forming an attraction surface is formed of metal or ceramics, the angle formed by the outer circumference of the base body and inner walls of penetration holes with the flat plane is defined at 80.degree. or less, and an aluminum nitride film is applied on the flat plane, outer circumference, and inner walls of penetration holes, thereby composing an attraction device such as wafer support member and vacuum chuck.
That is, according to the invention, the outer circumference of the base body and inner walls of penetration holes are formed in an upward taper at an angle of 80.degree. or less to the flat plane, so that an aluminum nitride film can be formed in a sufficient thickness in the outer circumference and inner walls of penetration holes. As a result, an attraction device extremely resistant to plasma and excellent in durability is obtained.
Also in the invention, a base body having penetration holes opening in a flat plane forming an attraction surface is formed of metal or ceramics, the boundary of the outer circumference of the base body and inner walls of penetration holes with the flat plane is chamfered, and an aluminum nitride film is applied on the flat plane, outer circumference, chamfered part, and inner walls of penetration holes, thereby composing a attraction device such as wafer support member and vacuum chuck.
That is, according to the invention, by chamfering the boundary of the outer circumference of the base body and inner walls of penetration holes with the flat plane, an aluminum nitride film can be formed in a sufficient thickness in the outer circumference and inner walls of penetration holes. Hence an attraction device extremely resistance to plasma and excellent in durability is obtained.
The invention relates to a wafer support member used in fixing, heating, filming, and processing of silicon wafer in a semiconductor manufacturing apparatus of the like.
In the semiconductor manufacturing apparatus, hitherto, the wafer support member used as stage of silicon wafer has been preferably used because flatness and parallelism of the processing surface required in fine processing of wafer in general vacuum can be easily realized.
Moreover, along with the sophistication of degree of integration of semiconductor element, a higher precision is required also in the wafer support member, and a ceramic-made wafer support member has come to be used.
Such high precision ceramic-made wafer support member has been manufactured by sintering integrally by incorporating a conductive layer forming an internal electrode in alumina ceramics (see Japanese Laid-open Patent 62-264638).
In the manufacturing process of semiconductor accompanied by vapor deposition or dry etching, a halogen gas derivative plasma is often used, and it is recently proposed to use aluminum nitride ceramics excellent in plasma resistance as the material for the wafer support member (Japanese Laid-open Patent 6-151332).
In the semiconductor manufacturing process using such plasma, various functions are required in the stage for mounting wafers on. For example, temperature control function for keeping the wafer temperature constant, electrostatic attraction function for keeping the wafer in tight contact with the stage, and plasma generating electrode are required.
If all these functions are realized by one stage, a compact and very efficient system will be made up.
Accordingly, it has been attempted to realize a wafer support member of all-in-one type incorporating all three metal layers of resistance heating element, electrostatic attraction electrode and plasma generating electrode, inside of a ceramic base body. Conventionally, such wafer support member was generally manufactured by printing metal paste for each electrode in a specific pattern on a green sheet of aluminum nitride, and laminating and sintering into one body.
However, when three different metal layers are assembled in a base body made of aluminum nitride, the base body may be cracked, or metal layers may be peeled or broken due to difference in thermal expansion in the sintering process.
In particular, the resistance heating element is a band pattern, whereas the electrostatic attraction electrode and plasma generating electrode are full-face patterns, and these two full-face patterns have a greater effect due to difference in thermal expansion on the ceramic base body.
To improve such problems as far as possible, it may be considered to reduce the electrode thickness to 30 .mu.m or less, but it causes to limit the high frequency electric power that can be applied to the plasma generating electrode.
That is, when plasma of over 200 W is applied to an electrode of 30 .mu.m or less, the electrode itself is heated abnormally, and sufficient etching or processing cannot be done, and ultimately the electrode may be burnt down or the ceramic base body may be broken down.
Accordingly, the invention composes a wafer support member by bonding a metal electrode plate in a thickness of 0.5 mm or more on a base body made of ceramics in a thickness of 3 mm or more, and forming an aluminum nitride film in a thickness of 0.01 to 0.5 mm on the surface of the electrode plate to be used as an attraction surface.
That is, in the invention, the electrostatic attraction electrode and plasma generating electrode are composed of metal electrode plates of 0.5 mm or more in thickness, and the ceramic base body and metal electrode plates are bonded in a buffer structure capable of mutually alleviating the difference in thermal expansion. Accordingly, the plasma generating electrode is an electrode plate having a sufficient thickness, and hence it is not heated abnormally or burnt down at high frequency.
According to the wafer support member of the invention, only one layer of a band thin film pattern of 20 .mu.m or less in thickness is buried in the base body as resistance heating element, an extremely high reliability is obtained same as in general ceramics heater.
The invention also relates to a wafer support member used in forming film or fine processing in a semiconductor wafer in a semiconductor manufacturing apparatus.
Hitherto, in the film forming device for forming a film on a semiconductor wafer or the dry etching device for fine processing in a semiconductor wafer, in a manufacturing process of semiconductor device, the wafer support member is used as the tool for holding the semiconductor wafer at high precision.
Moreover, along with the sophistication of degree of integration of semiconductor element, a higher precision is required also in the wafer support member, and a ceramic-made wafer support member has come to be used.
For example, as known so far, the ceramic base body for composing the wafer support member is formed by alumina ceramics or silicon nitride ceramics, and an electrode for electrostatic attraction is buried in the ceramic base body (see Japanese Laid-open Patent 62-264638).
Or, in the manufacturing process of semiconductor accompanied by vapor deposition or dry etching, a halogen gas derivative corrosive plasma generating plasma is used, and hence the ceramic base body is formed of aluminum nitride ceramics excellent in plasma resistance (Japanese Laid-open Patent 6-151332).
In the wafer support member used in semiconductor manufacturing process using plasma, aside from the electrostatic attraction function for attracting the wafer, temperature control function for keeping the wafer temperature constant and plasma generating function are required, and if all these functions can be integrated, a compact and very efficient wafer support member will be obtained, and hence an all-in-one type wafer support member incorporating all three metal layers of electrostatic attraction electrode, resistance heating element and plasma generating electrode inside of a ceramic base body is proposed.
However, when three layers are assembled in a ceramic base body, the base body may be largely warped or bent, or racked, or electrodes may be peeled or broken due to difference in thermal expansion in the sintering process.
In particular, the electrostatic attraction electrode and plasma generating electrode are full-face electrode patterns, and the ceramic base body was warped significantly by burying these two electrodes.
If the wafer is held by such wafer support member, therefore, flatness precision of the wafer was not obtained, and it had adverse effects on the semiconductor manufacturing process.
To improve such problems as far as possible, it may be considered to reduce the electrode thickness, but if the electrode thickness is less than 0.1 mm, it causes to limit the high frequency electric power that can be applied to the plasma generating electrode.
That is, to generate plasma, power of over 100 W must be applied to the plasma generating electrode, but if the electrode thickness is less than 0.01 mm, the plasma generating electrode is heated abnormally, and sufficient dry etching cannot be processed in the wafer, or the plasma generating electrode may be burnt down, or the ceramic base body may be broken down.
In the light of the above problems, the invention composes the wafer support member by forming a plurality of electrode in a thickness of 0.02 mm or more and maximum length of 5 cm or less on the surface of a ceramic base body, and forming a holding surface by covering the electrodes with an aluminum nitride film of 0.01 to 0.5 mm in thickness. In the invention, moreover, a resistance heating element for heating may be buried in the ceramic base body.
In the invention, a direct-current high voltage for electrostatic attraction and/or a high frequency electric power for generating plasma is applied to the electrodes so as to act as plasma generating electrode as well as electrostatic attraction electrode.
Moreover, in the invention, the ceramic base body is composed of ceramics of which volume resistivity is 10.sup.10 .OMEGA..multidot.cm or more and thermal conductivity is 20 W/m.multidot.K, and the electrode are composed of tungsten, molybdenum, or Kovar.
The invention further relates to a wafer holding device such as susceptor and wafer support member for holding the wafer such as semiconductor wafer and glass substrate for liquid crystal used in manufacturing process of semiconductor or liquid crystal substrate.
Hitherto, in the manufacturing process of semiconductor or liquid crystal substrate, in the CVD device for forming a thin film on a wafer such as semiconductor wafer and glass substrate for liquid crystal, the wafer holding device such as susceptor and wafer support member incorporating a resistance heating element was used in order to hold the wafer in the treating chamber and to heat the water to a necessary temperature for forming a film on.
In the susceptor 411, for example, a resistance heating element 413 is buried in a base body 412 made of a disk-shaped aluminum nitride sintered body as shown in FIG. 18, and a lead terminal 415 for feeding power to the resistance heating element 413 is provided in the lower surface of the base body 412.
In the wafer support member 421, moreover, an electrostatic electrode 424 and a resistance heating element 423 are buried inside a base body 422 made of a disk-shaped aluminum nitride sintered body as shown in FIG. 19, and a lead terminal 425 is provided in the lower surface of the base body 422 to feed power to the electrostatic electrode 424 and resistance heating element 423.
For bonding of the electrode 413, and lead terminal 415, (the lead terminals 415, 425 are shown in FIG. 20), an inner hole A is pierced in the lower surface of the base body 412, and a metalized layer B is formed on the surface of the inner hole A, and the lead terminals 415, 425 made of molybdenum, tungsten or other metal are bonded with a solder C.
To form a film on a wafer, however, the wafer holding device such as susceptor 411 and wafer support member 421 must be heated to a temperature over 600.degree. C., and hence the lead terminals 415, 425 of the electrodes 413 and 424 and heating element 423 directly bonded to the base bodies 411, 421 are heated to high temperature in the atmosphere to be oxidized. As a result, the resistance value of the lead terminals 415, 425 is largely changed, and the wafer holding device cannot be heated to specified temperature, and wire breakage may occur in a worst case.
In addition, the solder C for bonding the lead terminals 415, 425 to the base bodies 412, 422 reacts with oxygen in the atmosphere in high temperature state to corrode, and lead terminals 415, 425 may drop out.
Accordingly, it may be considered to cover the lead terminals 415, 425 and their junction with hard-to-oxidize material such as Ni, but the Ni film is poor in reliability, and wafer holding device having sufficient durability has not been obtained.
In the light of the above problems, the invention provides a wafer holding device incorporating a resistance heating element in a base body made of aluminum nitride sinter, and forming a lead terminal for feeding power to the resistance heating element in the lower surface of the base body, wherein at least the lead terminal and its junction are covered with at least one ceramic film selected from the group consisting of silicon carbide, silicon nitride, sialon, and aluminum nitride.
According to the invention, at least the lead terminal and its junction of the lower surface of the base body are covered with a ceramic film excellent in oxidation resistance, so that characteristic deterioration of lead terminal and corrosion of solder can be prevented for a long period.
In the invention, by using one of silicon carbide, silicon nitride, sialon, and aluminum nitride, similar to coefficient of thermal expansion of aluminum nitride sinter, among ceramics, as the ceramic film, tightness of contact with the base body at high temperature can be enhanced. Hence, if the wafer holding device is heated to high temperature, the oxygen in the atmosphere will not invade into the ceramic film, or the ceramic film will not be peeled off. In particular, when aluminum nitride is used as ceramic film, since it is the same material as the aluminum nitride sinter composing the base body, a higher reliability is achieved. Moreover, when the wafer holding device is installed in the treating chamber such as CVD device, the lead terminal and its junction are exposed to halide gas, but when coated with ceramic film made of aluminum nitride, the lead terminal and solder are free from corrosion even in halide gas atmosphere.